Sources of natural baddeleyite (ZrO2) are largely depleted. Zircon sand (ZrSiO4) is another and abundant source of zirconium but is very unreactive. Before zirconium can be retrieved from zircon sand, the zircon sand needs to be thermally or chemically decomposed. Thermal decomposition entails dissociation of zircon in plasmas or melting decomposition in melting furnaces.
Chemical decomposition can be achieved by reacting zircon with a source of alkali metal or a source of alkaline earth metal at elevated temperatures to form a fusion decomposed zircon product wherein the alkali metal or alkaline earth metal is fused with the zircon hereinafter referred to as alkali-fusion decomposed zircon product or AFDZ).
The AFDZ may be treated in a number of ways namely:    i) leaching with water to remove easily soluble alkali metal compounds and silicate values, especially where NaOH was used as the source of alkali metal in producing AFDZ;    ii) treatment with acid to neutralise alkali metal (where a source of alkali metal was used in producing AFDZ) and to form water soluble alkali metal salts and removal thereof by water extraction;    iii) treatment with rather concentrated acids to form water extractable zirconium salts.
A common way of beneficiating zircon comprises reacting zircon with sodium carbonate as a source of alkali metal to form AFDZ. The AFDZ formed is then comminuted, then treated with concentrated HCl and then leached with water to dissolve zirconyl oxychloride (ZrOCl2.xH2O) which forms in the process. The product is then filtered and sulphate is then added to the filtrate containing the zirconyl oxychloride to precipitate zirconium basic sulphate (hereinafter referred to as ZBS) with the formula Zr5O8(SO4)2. xH2O after further dilution and boiling for an extended time. Precipitation is usually from solutions containing 20 to 50 g of equivalent ZrO2 per liter, thus lengthy procedures involving large volumes are required which are disadvantages of this process.
Zircon also has a natural radioactive content with associated occupational health and environmental difficulties, already being experienced by those involved in the fine milling and the destructive processing of zircon, even though its radioactivity content is usually only about 50% of that of acid-leached milled baddeleyite. Waste disposal in zircon processing, as well as final disposal of zircon and related products, are being scrutinised for stricter control for materials with radioactivity equivalents above 10 Beq/g. This may lead to licensing requirements for transport and storage of zircon in addition to labelling of transport containers and also to licensing of plants handling zircon materials. The implication of the foregoing is an increased future demand for zirconia and zirconium products of relatively low radioactivity content.
It is an object of the present invention to overcome or at least reduce some of the above disadvantages.